Ruby provides a long life without wearing of the surface from abrasive materials.
For ball diameters greater than 3 mm, and lengths over 30 mm,ceramic stems offer stiffness comparable to steel but are significantly lighter than tungsten carbide.
Ceramic stemmed styli can also offer additional crash protection to your probe as the stem will shatter in a collision.
Straight styli are designed to inspect simple features where direct, unobstructed contact with a measured surface is possible.